Words.hs

{-
 -      ``Data/Random/Internal/Words''
 -}

-- |A few little functions I found myself writing inline over and over again.
module Data.Random.Internal.Words where

import Foreign
import GHC.IOBase

import Data.Bits
import Data.Word
import Control.Monad

{-# INLINE buildWord #-}
buildWord :: Word8 -> Word8 -> Word8 -> Word8 -> Word8 -> Word8 -> Word8 -> Word8 -> Word64
buildWord b0 b1 b2 b3 b4 b5 b6 b7
    = unsafePerformIO . allocaBytes 8 $ \p -> do
        pokeByteOff p 0 b0
        pokeByteOff p 1 b1
        pokeByteOff p 2 b2
        pokeByteOff p 3 b3
        pokeByteOff p 4 b4
        pokeByteOff p 5 b5
        pokeByteOff p 6 b6
        pokeByteOff p 7 b7
        peek (castPtr p)

{-# INLINE wordToFloat #-}
-- |Pack 23 unspecified bits from a 'Word64' into a 'Float' in the range [0,1).
-- Used to convert a 'stdUniform' 'Word64' to a 'stdUniform' 'Double'.
wordToFloat :: Word64 -> Float
wordToFloat x = (encodeFloat $! toInteger (x `shiftR` ( 41 {- 64-23 -}))) $ (-23)

{-# INLINE wordToDouble #-}
-- |Pack 52 unspecified bits from a 'Word64' into a 'Double' in the range [0,1).
-- Used to convert a 'stdUniform' 'Word64' to a 'stdUniform' 'Double'.
wordToDouble :: Word64 -> Double
wordToDouble x = (encodeFloat $! toInteger (x `shiftR` ( 12 {- 64-52 -}))) $ (-52)